Unwrapping a Result

Many functions in Rust have their return values wrapped in a result. The Result type is an enum with two variants, Ok and Err.

let result = std::fs::read_to_string("test.txt");

It is common to have to handle these cases separately. One can use a match statement, like so:

let content = match result {
  Ok(content) => content,
  Err(error) => panic!("Can't deal with: {}", error),
};

but this is in fact so common that there is a shortcut method called unwrap:

let content = result.unwrap();

Returning and the question mark

If we don't want to panic (and exit), we can return an error instead:

let content = match result {
  Ok(content) => content,
  Err(error) => return Err(error.into()),
};

Just like calling .unwrap() on a Result is a shortcut for match with panic! in the error arm, ? is a shortcut for a match with a return in the error arm:

let content = result?;

Sources

• Unwrapping
• Question mark